This invention relates generally to electronic video displays for presenting visual information such as in the form of alphanumeric characters and is particularly directed to a liquid crystal display (LCD) with light emitting diode (LED) backlighting.
User interactive devices typically provide status information to the user and, in turn, require user-initiated inputs for proper operation. These types of devices range from television receivers to remotely located, automatic banking, or cash, stations. The information provided to the user is generally in the form of alphanumeric characters. The display of this information may be continuous such as the selected channel of a television receiver or it may be periodic such as the current time. Regardless of the nature and type of information displayed, the display should provide information which is easily readable under a wide range of environmental conditions. Two of the more common types of displays make use of LCDs and LEDs. LCDs have the advantage of reduced cost, simpler installation, longer lifetime, and reduced power requirements. However, an LCD display suffers from the limitation that it is not visible in the dark and thus requires auxiliary lighting for night viewing. To this end, LCDs have been used in combination with incandescent bulbs as well as with LEDs which provide backlighting for LCD viewing in the dark. LEDs require less power and offer longer operating lifetimes than conventional incandescent bulbs.
Prior art LED backlighting arrangements for LCDs have suffered from various limitations. For example, the LEDs are typically positioned directly aft of the LCDs, causing the LEDs to appear as "hot spots" when the LCDs are viewed from the front. Other LED backlighting arrangements have made use of the light diffusing and internal reflection characteristics of transparent plastics such as plexiglass or Lucite. In this approach, the LEDs are positioned within recessed slots along an edge of the transparent plastic sheet which is aligned generally parallel to the plane of the LCDs. Internal reflection of the LED light within the plastic sheet which generally includes an angled outer surface results in the projection of the light within the plastic sheet onto the aft surface of the LCDs. While permitting the LCD display to be viewed in the dark, this approach requires that the LEDs extend beyond the periphery of the LCD display and thus requires considerable mounting space. In addition, the LED light exits the plastic sheet from surfaces other than the surface which is in facing relation to the LCD display, resulting in loss of some of the LED light and reduced backlighting efficiency.
The present invention overcomes the aforementioned limitations of the prior art by providing a domed light housing for an LCD display which is backlit by a plurality of LEDs. The housing confines all of the light emitted by the LEDs in forming a light conduit and directs this light onto the rear surface of the LCDs to provide backlighting for the LCDs when viewed from the front, wherein the LEDs are not directly visible from in front of the LCD display to eliminate LED "hot spots".